Recording films used in optical recording media, representative of which are DVD-RAMs, and in solid-state phase change memories (PCRAMs), are made of a chemical compound called “calcogen” whose main constituent is Te or Sb, where technology has been established whereby a pulsed laser beam such as semiconductor laser or pulse current is irradiated into a thin film made of this material having a thickness of approx. 20 nanometers to raise the film temperature to the melting point or above to cause phase change from crystalline to amorphous states, or vice versa.
Traditionally signals are recorded and regenerated by utilizing the differential reflectance (differential refraction factor) between crystalline and amorphous states.
Technologies relating to optical recording media using phase change are known (refer to Patent Literatures 1 to 8, for example). Today, ternary chemical compounds (Ge—Sb—Te materials) and quaternary chemical compounds (Ag—In—Sb—Te materials) that allow for at least one million recording-erasing cycles are already put to practical use.
In the meantime, coherent phonons are known to be generated when a femtosecond pulse laser is irradiated onto a solid matter (refer to Patent Literature 9, for example), and the amplitude of these coherent phonons is known to be controllable by optical pulse trains (refer to Non-patent Literatures 1 and 2). Studies are also conducted to shed light on the phase change process in phase change optical recording film materials (refer to Non-Patent Literature 3).